This invention relates to wire making and specifically to a method and fixture for filled billet packing wherein an entire pack is built up in a single step and wherein substantially even lateral forces are applied to wires or other elongate members within the billet by using filler rods at one or more places along the periphery of the pack.
The concept of using a filled billet manufacturing technique to make wires is known in the art. For example, U.S. Pat. No. 4,209,122, issued to Hunt on Jun. 24, 1980, discloses a method of making wires comprising the steps of providing a cylindrical can which has a closed end, an open end, and a central longitudinal axis; disposing a plurality of rods into the can through its open end in parallel relation to each other and parallel to the longitudinal axis; introducing a powdered filler material into the can to fill the spaces between the rods and the interior surface of the can; attaching a top to the open end of the can to thus complete a filled billet; heating the filled billet to a temperature approximately equal to the forging temperature of the rods; extruding the filled billet through an extrusion die to effect an area reduction in the cross-section thereof and of the rods therewithin; cooling the extruded filled billet; and removing the extruded can from around the extruded rods.
It is also known in the art to use a fixture that aids in the build-up of a group, or pack, of rods. The pack of rods is subsequently placed inside the extrusion can. An example of this is described in U.S. Pat. No. 4,777,710, issued to Hunt on Oct. 18, 1988. The fixture found in the ""710 patent allows build-up of the pack of rods in a row-by-row manner; with rods in each subsequent row fitting between the rods in the previous row.
However, fixtures in the prior art are limited to producing only half of the required pack of rods. The two half packs must then be aligned to mate with one another to create the full pack that is ultimately positioned inside the extrusion can. As a result of extrusion, the fixture described in the ""710 patent can cause the wires along the mating surfaces of the two halves to become flattened, due to difficulty in aligning the two halves, as shown in FIGS. 10-13. This results in loss of these wires as useful product or in a need to round up the wires by centerless grinding or rolling, which increases manufacturing costs, and may reduce yield on finished wire. In addition, due to the inability to seat the halves properly, the pack is not as densely built up and space is lost that otherwise would have been used to pack more rods.
A further disadvantage of the prior art fixtures, such as that described in the ""710 patent, is that extrusion causes wires on the periphery of the pack to become oval shaped or irregular, as shown in FIGS. 10-13. This is because there are unequal forces surrounding the peripheral wires during extrusion. The peripheral wires are in contact with other wires from inside the pack on their inner side(s), and filler powder on their outer side(s) that is placed between the pack of wires and the inner diameter of the can. Since the filler powder starts out at 40% to 60% of theoretical density and the wires are cast at essentially 100% density, the peripheral rods experience uneven forces during extrusion, and elongate in the weaker direction, toward the powder, where there is less support. Oval wires must be centerless ground or otherwise processed to round them up, resulting in loss of material, increased labor costs, and increased turn times. In some cases, the ovality is severe enough that the wires must be scrapped.
Another problem with the wire making method described in the prior art is that close packing of circular cross-section rods results in a hexagonal shaped pack. In order to densely pack the rods, rods are packed in rows such that the rods from one row rest in interstices between two rods of a second row and the pack naturally becomes hexagonal shaped. Because the hexagonal shaped pack must fit into the circular shaped extrusion can, space is wasted in the extrusion can around the pack, and as discussed above, gaps between rods and the inner diameter of the extrusion can cause rods to become oval shaped or otherwise misshapen during extrusion.
A further problem with the wire making method described in the prior art is rod end loss. During extrusion waste may occur at the ends of the rods of the pack when the extrusion can is pushed through a substantially smaller hole in the die of the extrusion press. This is true because rods on the inside of the pack often enter the plane of the extrusion die before the rods on the outside of the pack, causing uneven extrusion and unusable material on each end of the pack after extrusion. It is desirable to shape the pack such that all rods enter the plane of the extrusion die at the same time to substantially reduce or eliminate this waste.
In view of the foregoing limitations and shortcomings of the prior art, as well as other disadvantages not specifically mentioned above, it should be apparent that there exists a need in the art for a method and fixture for filled billet packing wherein a whole pack can be made at one time, eliminating a need to mate two halves, and wherein substantially even forces are applied to all rods or other elongate members within the billet.
It is therefore a primary object of the present invention to provide a method and fixture for filled billet packing that eliminates the misshapen wires along the mating surfaces of two half packs caused by misalignment of the two halves.
Another object of the present invention is to provide a method and fixture for filled billet packing that results in higher yields, lower manufacturing costs, and shorter manufacturing turn time.
It is a further object of the present invention to reduce the ovality of peripheral wires in a wire pack, by reducing the stress differential around the peripheral rods during extrusion.
It is another object of the present invention to create a rounder pack shape that conforms more closely to the inner diameter of the can, resulting in more uniform, hydrostatic forces on all rods.
It is a further object of the present invention to provide a means for shaping a pack of wires that reduces or eliminates waste of the ends of the rods of the pack after extrusion.
Briefly described, these and other objects are accomplished according to the present invention by providing a method and fixture for filled billet packing wherein rods are placed within a fixture having a substantially symmetrical area for accepting rods therethrough that can accommodate an entire pack of rods, and clamping means that apply lateral force to the pack to densely pack the rods. The fixture contains a shaping tool for creating a pack that is substantially cylindrical in shape which results in a pack whose cross-section more closely approximates the cylindrical inner diameter of an extrusion can, resulting in a more densely packed billet. The shaping tool also reduces or eliminates waste at the ends of the rods of the pack after extrusion. Dummy rods may be placed at one more places along the periphery of the pack within the fixture to help maintain tight packing. Filler rods are placed around the periphery of the pack in the extrusion can to apply lateral force to the peripheral rods that is substantially equal to the lateral forces imposed by rods inside the pack.
Additional benefits and advantages of the present invention will become apparent to one skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.